The present invention relates to the field of hydrodynamic bearing assemblies, and more specifically, to a design which allows for easier assembly of the conical bearing as well as for easier filling of the bearing with fluid.
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle. The information is accessed by means of read/write heads generally located on a pivoting arm that moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by means of an electric motor generally located inside a hub that supports the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted by means of two ball or hydrodynamic bearing systems to a motor shaft disposed in the center of the hub. Generally, such motors include a stator comprising a plurality of teeth arranged in a circle. Each of the teeth support a plurality of coils or windings that may be sequentially energized to polarize the stator. A plurality of permanent magnets are disposed in alternating polarity adjacent the stators. As the coils disposed on the stators are sequentially energized in alternating polarity, the magnetic attraction and repulsion of each stator to the adjacent magnets cause the spindle to rotate, thereby rotating the disc and passing the information storage tracks beneath the head.
The use of hydrodynamic bearing assemblies in such drive systems has become preferred due to desirable reductions in drive size and noise generation as compared to conventional ball bearing drive systems. In hydrodynamic bearings, a lubricating fluid, such as oil or air, functions as the bearing surface between a base or housing and a spindle or hub. As the lubricating fluids require small gaps between the stationary and rotating members in order to provide the support, stiffness and lubricity required for proper bearing operation, conventional drive components and assemblies typically require tight tolerances and demand precision assembly methods. Such demanding tolerance and assembly control results in increased part and assembly costs along with an increased level of quality control to ensure proper drive operation.
Thus the problem presented is to make hydrodynamic bearing and especially a conical bearing, which is easier to assemble and fill with bearing fluid.
Present day conical bearing design includes a sloping outer surface on the cone which is positioned on the shaft. This makes it quite difficult to accurately push the bearing cone onto the shaft and accurately locate it as the positioning tool must be pressed against a sloping surface. Current conical bearing design also makes the bearing hard to fill. The gap between the shield which must be placed over the top of the bearing cone and supported from the sleeve is very small. This makes it hard to insert a needle or the like to feed the bearing with oil. The alternative is to leave a small hole extending through the shield. However, this creates the related problem of having a hole through the shield which will remain open after the bearing has been filled with fluid. Thus it is always possible that impurities could find their way in through this hole, however small, and find their way into the fluid. Further, if instead an effort is made to insert oil between the end of the shield in the other diameter of the shaft, oil may get stuck between the shaft OD and the shield ID. Further, current design using a conical outer surface places the meniscus of the oil or fluid which fills the bearing quite close to the gap between shield and shaft, presenting the opportunity, especially if a shock occurs, for some oil to reach the shaft and migrate along the shaft out of the bearing.
Therefore, the problem presented is to develop and adopt a design to make such a conical bearing easier to assemble and less susceptible to fluid migration.
The present invention provides method and apparatus for easily assembling a conical bearing on a shaft.
The present invention further provides a modified shield plate overlying the conical bearing to make filling of the hydrodynamic bearing easier, and to diminish the likelihood of loss of fluid.
A further advantage of the invention is that by adopting the invention, the possibility of oil evaporation is lower, and any particles that exist in the fluid may be more easily collected outside the fluid bearing gap.
In summary, according to the present invention, the design of the cone which is pressed onto or otherwise affixed to the shaft to cooperate with the sleeve to form a conical hydrodynamic bearing is modified to provide a flat surface at the axially outer end of the cone most distant from the conical surface which is used to form the conical fluid bearing in cooperation with the sleeve and the intervening fluid.
Further, the sleeve surface facing the upper conical or angled surface of the bearing cone is modified to diverge more sharply away from the upper conical surface of the bearing cone, or to simply be spaced further away. In this way, a larger fluid reservoir is formed between the surface of the sleeve and the outer upper surface of the bearing cone, diminishing the possibility of oil evaporation and oil loss.
Finally, a relatively flat shield is supported from the sleeve overlying the flat upper surface of the cone, making this shield simpler to fabricate and install with the necessary tolerances relative to the cone which is imposed on the sleeve.
The use of a bearing cone having a secondary angular surface which cooperates with the surrounding sleeve to form a larger reservoir, and ends in a substantially flat axially distal surface allows the cone to be more easily pressed onto the shaft by presenting a surface that is normal or substantially normal to any pressing force imposed. This normal surface or substantially normal surface also makes it easier to set the axial height of the cone.
The divergence of the upper bearing cone surface from the surrounding sleeve also allows for filling the bearing before the shield is installed. This solves the problem of trying to fill the bearing through a small hole either directly in the protective shield or between the protective shield and the outer diameter of the shaft. Not having the hole in the shield also lowers the likelihood of evaporation or splash loss of fluid from the conical bearing.
Other features and advantages of the invention as well as manner in which the above described features and benefits of the present invention are attained can be understood by reference to the embodiment thereof, which is illustrated in the appended drawings. It is to be noted, however, that the drawings illustrate only an exemplary embodiment of the invention and are not considered limiting in its scope, for the invention may admit to other equally effective embodiments.